Solder analyzer



Dec. 26, 1950 F. L. KUREK SSOLDER ANALYZER Filed June 15, 1945 h'me Minutes u 9.5.. "tun-Ev. 5:: ULw O Patented Dec. 26, 1950 UNITED STATES PATENT OFFICE SOLDER ANALYZER Francis L. Kurek, Chicago, Ill., assignor to 0011- tinental Can Company, Inc., New York, N. Y.,

a corporation of New York Application June 15, 1945, Serial No. 599,738

11 Claims. I

It is often desirable to determine the constitution of mixtures with respect to a variable ingredient thereof, without lengthy chemical or physical tests of the material.

For example, alloys composed of 2 percent of tin and 98 percent of lead have been employed for soldering seams on tin plate. During operation on machines for soldering, the tin content gradually builds up from the tin on the tinplate, and if the tin content exceeds 4 percent, there is danger of forming open laps and consequently leaky seams. Likewise, such increases in tin content represent losses of tin. The practice therefore is to dilute the solder bath with a pure lead, so that it is possible to solder more cans with a given amount of tin. The more frequently proper additions are made, the greater is the tin saving. It is therefore necessary to make frequent checks of the tin content of the solder baths; sometimes these checks mustbe made as often as every hour. A physical determination may be made by density methods, but these are slow and require a skilled operator and an accurate analytical balance. Chemical analyses may be performed, but these are slow and expensive.

It has been found that such determinations may be accomplished with materials which have a transformation point at some critical temperature, by comparing the unknown or specimen to be tested with a reference material which likewise has a transformation point closely adjacent in temperature to the transformation point of the unknown by causing the heat content of a standard quantity of the unknown and the heat content of the reference material each to change at a regular rate so that the "unknown and the reference material come to their critical temperatures and pass concurrently through their respective transformation points. A transformation point of a material is a temperature at which a given body of the material undergoes a change in heat content without any accompanying change in temperature and without any necessary change in the external pressure to which the material is being subjected.

For example, in performing a determination of the aforesaid tin-lead alloy, elemental lead may be used as a reference material, and standard quantities of the molten lead and molten tinlead alloysare permitted to cool. The elemental lead reaches its transformation point and begins to solidify, remaining at the same temperature until solidification is accomplished; meanwhile giving off its latent heat of fusion. Meanwhile,

the specimen of unknown continues to dropin temperature until it likewise reaches its transformation point, at which the unknown also begins to solidify and maintains the temperature of this transformation point until it has solidified; meanwhile giving off its latent heat of fusion. The temperatures of these transformation points differ, and the critical temperature of the unknown is lower than the critical temperature for the elemental lead because of the tin which is present and which acts to depress the solidifying point. Thus, for the interval of time dependent in part upon the rate of loss of heat from the bodies of material, each material remains essentially at a fixed temperature; and a determination can be made of this temperature difference. This temperature difference can then be used in computing the percentage of tin present.

In accordance with the present invention, this procedure is performed by employment of a simple, compact, and quickly operated apparatus in such a fashion that the determinations may be made by an operator having no fundamental knowledge of the underlying principle, and without necessity for this operator to accomplish any corrections for room temperature or the like. By employment of this apparatus, a determination can be made in a few minutes, the apparatus cleared quickly, and made ready for a further analysis in short order.

An illustrative form of practicing the invention is shown on the accompanying drawings in which:

Figure 1 is a perspective view of the apparatus;

Figure 2 is a cross sectional view through the holder forthe unknown specimen and for the reference material;

Figure 3 is a circuit diagram;

Figure 4 are graphs indicating the behavior during determination. 7

When most substances melt they take up a quantity of heat defined by a characteristic known as latent heat of fusion.

the entire substance has passed from the solid to liquid condition by its change of state. Correspondingly, as the liquid cools, save and except as supercooling effects may have intervened it attains a transformation point, known as the solidification point which, for most substances In melting, save and except as superheating efiects may is the same as the melting point. In general, transformation points are very closely marked and are set out in tables of constants.

In Figure 4 is illustrated the behavior of commercially pure or 100% lead which is shown in physical tables as having a melting point of, very closely, 621 degrees F. If this elemental lead is heated to a temperature of say 675 degrees F., it melts and becomes a liquid. If a body of this molten lead is permitted to cool, the graph comparing time and temperature is of the nature shown in Figure 4. As the material cools from the time-temperature point It), the material decreases in temperature steadily as represented by the line H until the temperature has dropped to about 621 degrees F. The lead now begins to solidify, yielding ofi its latent heat of fusion, and for a time the temperature remains essentially constant at 621 degrees F., from point [2 to point [3. After this, or when the latent heat of fusion has been lost, the elemental lead has become a solid, and it begins to decrease in temperature again, as represented by the line I4.

By comparison an alloy of tin and lead, having less than ten percent of tin present, behaves much the same as the elemental lead, except that the transformation point is at a lower temperature. Thus, if a specimen of such an alloy, containing for example four percent of tin, is permitted to cool from the time-temperature point It), it origin-ally cools as indicated by the line 15. Owing to the presence of the tin, it does not undergo a transformation at about 621 degrees, but continues to cool to a temperature of about 600 degrees and then at the point It in Figure 4, it likewise begins to indicate transformation by solidifying while giving off its latent heat of fusion. For a time, therefore, the graph ll represents the time-temperature condition of this alloy. Ultimately, when it is solidified, it also again begins to drop in temperature, as illustrated by the line [8.

The transformation conditions between points l2 and ['3 for the elemental lead, and as indicated by the line I! for the tin-lead alloy, thus extend parallel to one another for a period of time, and represent temperature diiference's of the two bodies. Thus, the standard specimen (here, lead) and the unknown specimen (here, a tin-lead solder) concurrently pass their respective transformation points.

A graphic indication of these temperature differences is shown by the lower portion of Figure 4, Where at time-temperature point In the specimen of unknown and the reference material are at the same temperature. By preference the body of reference material is caused to decrease in temperature more rapidly than the alloy being tested, wherewith the portion 20 of the graph has a downward inclination. As soon as the elemental lead reaches its transformation point and begins to solidify, the temperature difference increases at a rate dependent upon the slop of line 15, this fact being represented in the lower portion of the figure by the line 21. Thereafter, when the tin-lead alloy reaches its own transformation point and begins to solidify, the two ma terials remain at an essentially fixed temperature difference for a period of time, as represent ed by the line 22. As soon as the elemental lead has totally solidified, it b gins to again drop in temperature and the temperature difference decreases rapidly as indicated by the line 23. The foregoing preference for having the elemental,

lead specimen decrease in temperature at a greater rate than the unknown specimen, has the result or causing the temperature difference between the two to be reversed, so to speak, as illustrated by the line 25. passing below the zero reference line, after both specimens hav become solid.

Hence, by determining the temperature diiferenc'e, which is essentially constant during the time represented by line 22, it is possible to determine the relation of the two transformation points, and to compute the composition of the unknown. In the illustrative apparatus the constancy endures for from about 5 seconds with 10 percent tin alloys to about 1 minute for 0 percent tin, which is ample for the reading of the maximum current flow effect.

The procedure includes the determination of the temperature difference between the standard and unknown specimens at the time of concurrent transition through the transformation points of temperature. It will be noted that the temperature difference, and not the absolute temperature of either transformation, is employed for the determination.

The illustrative apparatus is composed of a support having two chambers, one for the reference material and the other for the unknown together with a thermo-electric battery which is responsive to the individual temperatures in these two bodies, and a meter for determining the current efiect produced in the thermo-electric battery.

In Figure 1, a handle 38 on a hollow stem 3| supports a structure having two chambers. As shown in Figure 2, the structure has a central 'att'achment portion 32 into which is threaded a chamber member 33 for totally enclosing a standard amount of the reference material 34. Likewise connected to the central portion 32 is a second chamber -35 which has a slot or opening 36 therein by which a standard amount of the unknown may be taken up in the chamber.

A thermo-electric battery or thermo-pile, comprised in the illustrative form of six units, has its alternate junctions located in the well 38 of chamber 33, with the intervening junctions in the well 3'5 of chamber 35. Thus, the successive junctions are exposed to the temperatures prevailing in the reference material and in the speci= men of unknown.

As shown in Figure 3, this thermopile may be formed of the constantan wires 40 alternated with the Chromel wires ii, the junctions being welded. The end junctions are connected to the copper conductors =32, 43 which lead to an ammeter fi l. It is preferred to provide a normally closed push button switch 5 across the terminals of the meter, so that the meter may only read when the push button is depressed whereby to avoid damage to the meter by the heavy current flow when the thermopile is exposed on the one hand to cold lead, and on the other hand to molten alloy; this arrangement also having the virtue of avoiding any variation by contact resistance when the switch is open for deriving the indication.

The meter, in the described form, may be a milliammeter provided with a scale graduation representing the percentage of tin present.

In use, the operator supports the meter M by a neck strap 56. The double-celled chamber structure 33, is dipped into a solder bath so that solder flows through the hole 36 and fills the chamber '35. Ihe structure is held in the solder bath until the elemental lead is melted,

this condition being ascertained by momentarily depressing the switch 45 and observing whether the meter needle indicates zero. :So long as the elemental lead is not at the temperature of the solder bath, this difierential causes a thermoelectric current to flow from the battery, andthe meter indicates the fact by indicating a reverse flow, i..e., below zero. As soonas the contents of the two chambers are at the same temperature, as indicated by point H1 in Figure 4, and by a zero reading of the meter, the structure is withdrawn from the solder bath and held in open air. Heat is now radiated from the chambers 33,135 at a substantially regular rate, wherewith the materials cool at the rates indicated by the lines H, ll"; of Figure 4. Upon depressing the switch 45 this efiectis shown on the meter by a relative movement of the pointer toward the left in Figure 3, representing the downward slope of line'2fl. As soon as the reference material reaches its transformation point, the meter needle begins to swing toward the right or clockwise in Figure 3, and continues so to move until the unknown material has likewise reached its transformation point. Upon this event, the meter needle remains steady for the time indicated by line 22, this being a maximum and steadyreading which may endure for up to a minute with the illustrated apparatus as described above. During this time the meter needle points to a percentage of content which represents the com" position of the alloy and the operator enters this upon a report sheet, as indicating the prevailing compositioninthe particular solder bath.

Ultimately, it cooling is allowed to continue,

the alloy itself will solidify and the meterreading will fall rapidly as indicated by line 23, and then pass to a negative reading as indicated by line 24, with this indicated construction.

As soon as thereading atline .22 has been effected, theoperator can pourthe solder from the chamber .35 back into the solderbath. If the contents ,have solidified, the head 33-3 E* be immersed in the solder bath to produce a melting of the alloy so thatit may be poured back into the solder bath .for cleaning the apparatus and preparing itfor a further determination.

It is preferred to form the parts which are to be exposed to the solder .of a material which is not wetted by the solder,.such as stainless steel.

It will benoted that no manual or computative compensation or allowance forroom temperature, etc., need be made. In practice, it has been found that the tin content of tin-leadsolders in the range from to 5% of tin can be de termined to within 0.1% of tin and in the ,range from 5 to of tin can be determined to within an accuracy of 0.2% of tin, with the illustrative form of apparatus. The determinationsror leadtin alloys, for example, can be conducted up to 2.0 percent or higher (/2 percent accuracyl provided care is taken to assure that the standard and unknown specimens have concurrent transformations for a suflicienttime duration for readmg.

It is preferred to have the volume of elemental lead, in this illustrative form, less than the volume of alloy, e. g., about two-thirds of the weight of the latter; so that the heat :content in the elemental lead will be slightly less than that in the solder alloy, asan assurance that the lead will completey solidify before the alloy completely solidifies. This causes the line 22 to be terminated by the downwardline 23: whereas if the lead were permitted to remain molten after the solder 1. alloy solidified, the temperature difference would increase until the lead solidified, and therewith an upward jog .or .kick-up" would be present between the lines22 and .23. With the preferred arrangement, therefore, the line 22 representsthe maximum temperature difference, and this line corresponds to a static position of the meterpointer at a value representingthe temperature difference and thus the composition of the solder alloybeing tested.

Inthe illustrative form, the chamber 33 forthe elemental lead may be 1 inch .long inside and three-fourths inch in inside diameter; while the cupproviding the solder chamber .35 is correspondingly 1 inches long inside and /aainch in inside diameter, the wall thicknesses being.

/s4th of aninch for each cup. In this structure, the spacing between the inner or adjacent end walls of the chambers 33, 35 was approximately Anths of an inch, and the wells .31, 33 were each of stainless steel tubing with an insiderdiameter of /a2nds of an inch and an outside diameter of /s2nds of an inch with an inside ex.- posed length for the lead cup of /elth pinch, and for the solder cup of /sith inch. This size has beenfound convenient for use with the solder baths or pots of can making machines. The lead is melted and poured .into its chamber and the chamber sealed, preferably while thelead isstill molten and while subjected to evacuation: thisleaves a fhead space of about 1 6th inch to avoid any disruption of the cup by any .difiereneeein thermal coefficients of expansion. With this structure, 65 grams of lead and 110 grams of solder are used in the respective cups. The ratio in volume or weightis not critical: and it has been found that the illustrated device will operate satisfactorily even when the amount of solder alloy is as low as grams.

With these sizes of parts, the six thermo-couple sections were found to give a sufiicient voltage, for solder compositions between 0% and 10% of tin, for operating an inexpensive milliammeter of a rugged construction. Obviously, the number of couples in the thermo-battery of thisillustrative form may be varied. Withfewer couples, a more sensitive meter is required for the particular investigation of the specific alloys; while the employment of more thermo-couple elements leads to a higher voltage effect but with agreater temperature lag due to the heat capacity of the elements and their coverings. In practice, it has been found desirable to use a heat-resistant insulation, such as glass thread, between the .ele-

. ments: this insulation acts to delay the change of temperature of the thermo-couple elements, so that a slight lagoocurs, with the advantageoi preventing sudden and irregular pointer movements at the meter upon minor localized temperature changes.

The form 00f apparatus described above em ploys elemental lead as the reference material for determining the tin content in tin-lead alloys. Obviously, any other reference material may be used which @has a transformation point-of te perature near the transformation point of "the substance to-be tested. For examplawithproper change of the meter scale, the reference material may be a tin-lead alloy which solidifies either above or below the solidification point or the specimen to be tested. In either case, the meter reading will be in proportion to the temperature difierence between the solidification or trans formation points. When the reference material solidifies below the solidification point of the.

specimen to be tested, obviously the current flow is in the opposite direction, and the meter may be directly calibrated to read to the left from center instead of to the right as indicated in Figure 2.

It is obvious that the invention is not limited to the illustrative form set out, but that it may be practiced and the procedure employed by using apparatus other than the illustrative thermo-electric battery and meter for determining the temperature difference between the transformation points.

What I claim is:

1. An apparatus for use in determining the constitution of a material having a transformation point of temperature, comprising a, support ha ing two chambers of which one encloses a predetermined amount of a reference material having a transformation point near the first said transformation point and the other provides a receptacle for a predetermined amount of the material to be tested, said chambers each including heat-- conducting walls through which heat can pass to and from the contents of the respective chamber whereby to cause the materials therein to undergo changes of heat contents whereby they pass through their transformation points at least partially concurrently and means for measuring the temperature difference between the materials in said chambers.

2. An apparatus for use in determining the constitution of a material having a transformation point of temperature, comprising a support having two chambers of which one encloses a predetermined amount of a reference material having a transformation point near the first said transformation point and the other provides a receptacle for a predetermined amount of the material to be tested, said chambers each including heat-conducting walls through which heat a can pass to and from the contents of the respective chamber whereby to cause the materials therein to undergo changes of heat contents whereby they pass through their transformation points at least partially concurrently and a I thermo-electric battery having one junction positioned relative to said one chamber so as to be heated by said reference material to substantially the temperature of said reference material and having the next junction thereof positioned relative to said other chamber so as to be heated by said material to be tested to substantially the temperature of said material to be tested, and electrical indicating means responsive to the potential of said thermo-electric battery.

3. An apparatus for use in determining the constitution of a material having a transformation point of temperature, comprising a support having two receptacles, one said receptacle holding a predetermined amount of a reference material having a transformation point near the first said transformation point, the other receptacle being adapted for holding a predetermined amount of the material to be tested and circuit means including devices responsive to the prevailing temperatures in said receptacles for delivering a current proportioned to the temperature difference between said reference material and said material to be tested, and also including a device for indicating the prevailing current flow.

4. An apparatus for use in determining the constitution of a material having a transformation point of temperature, comprising a support having two chambers of which one encloses a predetermined amount of a reference material hav '8 ing a transformation point near the first said transformation point and the other provides a receptacle for a predetermined amount ofthe material to be tested, a thermo-electric battery having one junction positioned so as to be heated by said reference material to substantially the temperature of said reference material and having the next junction thereof positioned so as tov be heated by said material to be tested to sub-. stantially the temperature of said material to be tested, and circuit means through which flowsthe thermo-electric current consequent upon temperature differences in said materials, said circuit means including a device for indicating the pre vailing current effect.

5. An apparatus for use in determining the constitution of a material having a transformation point of temperature, comprising a support having two chambers of which one encloses a,

predetermined amount of a reference material having a, transformation point near the first said transformation point and the other provides a receptacle for a predetermined amount of the material to be tested, a thermopile comprising a plurality of elements having junctions positioned relative to said one chamber so as to be heated by said reference material to substantially the temperature of said reference material and hav-. ing other junctions positioned relative to said.

other chamber so as to be heated by said material to be tested to substantially the temperature of said material to be tested, said elements being connected to deliver a thermo-electric current proportionate to the prevailing temperature difference between said materials, and circuit means through which flows said thermo-elcctric current, said circuit means including a device for indicating the prevailing current effect.

6. An apparatus for use in determining the constitution of tin-lead alloys comprising a support having two chambers of which one encloses a predetermined amount of elemental lead and the other is constructed and arranged to receive a predetermined amount of the alloy to be tested, a thermo-electric battery having successive junctions of unlike thermo-electric properties, alternate junctions being positioned relative to said one chamber so as to be heated by said elemental lead to substantially the temperature of said elemental lead and the intervening junctions being positioned relative to said other chamber so as to be heated by said alloy to substantially the temperature of said alloy whereby a thermoelectric current iiows from said battery in correspondence to the prevailing temperature difference between said lead and said alloy, and circuit means connected with said battery and including a device for indicating the prevailing current effect produced when the lead and the alloy are both passing through their respective transformation points, said chambers each including heatconducting wa;ls through which heat can pass to and from the contents of the respective chamber whereby to cause the materials therein to undergo changes of heat contents whereby they pass through their transformation points at least partially concurrently.

7. An apparatus for use in determining the constitution of tin-lead alloys comprising a support having two chambers of which one encloses a predetermined amount of elemental lead and the other is constructed and arranged to receive a predetermined amount of the alloy to be tested, said last named amount being sufliciently larger than the amount of the elemental lead to cause the lead to completely solidify before the alloy completely solidifies, a thermo-electric battery having successive junctions of unlike thermoelectric properties, alternate junctions being positioned relative to said one chamber so as to be heated by said lead to substantially the temperature of said lead and the intervening junctions being positioned relative to said other chamber so as to be heated by said alloy to substantially the temperature of said alloy whereby a thermo-electric current flows from said battery in correspondence to the prevailing temperature difference between said lead and said alloy, the greater amount of alloy to be tested being effective by its greater mass/radiating surface ratio to cause the said amount to cool at a slower rate than the rate of cooling of the elemental lead, and circuit means connected with said battery and including a device for indicating the prevailing current effect produced when the lead and the alloy are both passing through their respective transformation points, said chambers each including heat-conducting walls through which heat can pass to and from the contents of the respective chamber whereby to cause the materials therein to undergo changes of heat contents whereby they pass through their transformation points at least partially concurrently.

8. A process of determining the constitution of a material having a transformation point of temperature, which comprises causing by independent heat exchange a quantity of the material and a quantity of a reference material having a transformation point near the first said transformation point to change their respective heat contents and at least partially concurrently pass through their respective transformation points, and determining as a value of one component of the material being tested the temperature difference between the said quantities of material while they are concurrently passing through their transformation points.

9. A process of determining the constitution of a material having a transformation point of temperature, which comprises causing by independent heat exchange a quantity of the material and a quantity of a reference material having a transformation point near the first said transformation point to change their respective heat contents and at least partially concurrently pass through their respective transformation points,

employing the temperature difference between the said quantities of material while they are concurrently passing through their transformation points to produce a thermc-electric current having a value varying with said temperature difference, and measuring the said thermo-electric current. i

10. A process of determining the tin content of tin-lead alloys, which comprises heating a quantity of lead and a quantity of the lead-tin alloy to be tested to a temperature above the melting points of both said materials, cooling the said quantities concurrently at rates such that the two quantities at least partially concurrently pass through the respective transformation points of the materials, and measuring the temperature difference between the materials while both are concurrently passing through their transformation points.

11. An apparatus for use in determining the constitution of a fusible material having a latent heat of fusion, comprising a handle, two receptacles mounted on said handle adjacent one another, one said receptacle having an opening through which may be introduced a charge of the material to be tested, the other said receptacle having a cavity for containing a charge of a reference material having a transformation point of temperature near the fusion point of the said fusible material and having walls totally enclosing said cavity whereby said receptacles may be immersed in a molten mass of said fusible material without access of said fusible material to said cavity, protective wells in each said receptacle, a thermo-electric battery comprising joined elements with alternate junctions thereof located in one and the other well, and conductors connected to and leading from the ends of said battery.

FRANCIS L. KUREK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,189,785 Brown July 4, 1916 1,285,920 Brown Nov. 26, 1918 1,550,272 Martin Aug. 18, 1925 1,911,191 Harsch et a1 May 30, 1933 

3. AN APPARATUS FOR USE IN DETERMINING THE CONSTITUTION OF A MATERIAL HAVING A TRANSFORMATION POINT OF TEMPERATURE, COMPRISING A SUPPORT HAVING TWO RECEPTACLES, ONE SAID RECEPTACLE HOLDING A PREDETERMINED AMOUTN OF A REFERENCE MATERIAL HAVING A TRANSFORMATION POINT NEAR THE FIRST SAID TRANSFORMATION POINT, THE OTHER RECEPTACLE BEING ADAPTED FOR HOLDING A PREDETERMINED AMOUNT OF THE MATERIAL TO BE TESTED AND CIRCUIT MEANS INCLUDING DEVICES RESPONSIVE TO THE PREVAILING TEMPERATURES IN SAID RECEPTACLES FOR DELIVERING A CURRENT PROPORTIOEND TO THE TEMPERATURE DIFFERENCE BETWEEN SAID REFERENCE MATERIAL AND SAID 